In the second part of Wikibooks (see part I on isomerism) again hundreds of Wikipedia editors have contributed to bring you the ultimate wikibook on organic reactions:

Open here: Wikibooks/Organic_Reactions.pdf (10 MB, 184 pages)

This wikibook contains all the organic reaction types (largely Jerry March classification) and a selection of organic reaction such as Wittig reaction and Aldol reaction. If the timestamp for the first edit in the organic reaction article is a measure, this project started almost 7 years ago at 4 minutes past 10 A.M. January 22 2003 by an anon user possibly associated with the University of Munich.